In a study recently published in Paleoceanography, Khider et al. (2014) write that centennial- to millennial-scale variability has been identified in a number of Holocene climate archives, citing O'Brian et al. (1995), Bianchi and McCave (1999), deMenocal et al. (2000), Viau et al. (2002), Mayewski et al. (2004), Wang et al. (2005) and Jansen et al. (2007), while noting that examples of this variability include the 8.2 kyr event and the Medieval Warm Period-to-Little Ice Age cooling of the past 1000 years, to which could be added the subsequent Little Ice Age-to-Current Warm Period warming. And so the question arises: What phenomenon has been behind these changes?

In addressing this question, the three researchers investigated "the relationship between tropical Pacific and Southern Ocean variability during the Holocene using the stable oxygen isotope and magnesium/calcium records of co-occurring planktonic and benthic foraminifera from a marine sediment core collected in the western equatorial Pacific." And at the conclusion of their analyses of the data with which they worked, they state that "although we cannot totally discount the volcanic and solar forcing hypotheses, we are left to consider that the most plausible source for Holocene millennial-scale variability lies within the climate system itself." In particular, as they continue, "Upper Circumpolar Deep Water (UCDW) variability coincided with deep North Atlantic changes, indicating a role for the deep ocean in Holocene millennial-scale variability."

And so it is that in the case of the most recent phase of Holocene millennial-scale climate variability - i.e., the Little Ice Age-to-Current Warm Period warming - we must also consider the likelihood that it, too, may have been driven by the very same force or forces that were responsible for all of the many other episodes of millennial-scale climate change of the Holocene, which were clearly not driven by changes in the air's CO2 content, as may be readily understood in light of the CO2 vs. time plot of the data presented below, where it can be seen that although there are large gaps between some of the data points in the record, it appears that the atmosphere's CO2 concentration varied but little until the rapid rise of the last century, so as to make it impossible for CO2 fluctuations to have had anything at all to do with prior warming or cooling events of the Holocene, which implies that something other than the historical rise in the air's CO2 content has likely been responsible for the most recent and concurrent warming of the globe, since such has had to have been the case in similar century-scale warmings of the past.